The social media giant is blocking minors from seeing postings of gun sales and will take down sales that don't require a background check or cross state lines.

The change is a win for groups like Moms Demand Action for Gun Sense in America and Mayors Against Illegal Guns, which have been lobbying for more restrictive gun policies at businesses including Starbucks, Staples and Facebook.

"On the same site that people are sharing birthday parties and family reunions, there are photos of AK-47s," says John Feinblatt, chairman of Mayors Against Illegal Guns. "This is not in the bowels of Facebook. This is upfront, center and easy to access."

Until now, Facebook regulated only paid ads and sponsored stories, which could not promote weapons of any kind. Images of weapons are generally acceptable as long as the weapon is not pointed directly at the viewer. User posts could say almost anything.

Although the focus is on gun sales, the new changes will apply to the promotion of other restricted items like alcohol or adult products.

Over the next few weeks, Facebook will begin deleting gun sale posts that are flagged by users, indicating that the post is against Facebook policy. Administrators of pages promoting gun sales will be required to put gun sale information in their "About" section.

The changes will extend to Instagram, where someone searching for a hashtag related to gun sales will get a pop-up requiring them to acknowledge the relevant laws that apply to them before they can see search results.

New York Attorney General Eric Schneiderman has been pushing Facebook to adopt these restrictions and was an adviser to Facebook in constructing the policy. "Responsible social media sites know that it is in no one's interest for their sites to become a 21st century black market in dangerous and illegal goods that place our families and communities at risk," Schneiderman said.

Moms Demand Action and Mayors Against Illegal Guns posted a petition in late January on websites including Change.org and SumOfUs.org proclaiming, "It's a social media gun show that we can't allow to go on any longer." By Wednesday morning, the petitions had more than 230,000 signatures.

Facebook gun traders responded with their own petition, saying "It's not OK to target only firearm enthusiasts for excessively restrictive rules." The petition has more than 8,900 signatures.

Similar petitions are circulating on a Facebook page called Guns For Sale that has more than 200,000 likes and thousand of posts from buyers and sellers. One, titled "Facebook: stay fair — don't cave in to the anti-gun demands!" was posted by Stanton McCandlish, 45, of Oakland, Calif.

"There is no smoking gun here of big groups of Facebook users doing something wrong that requires some regulation," McCandlish says. "But Facebook is a private company. I guess if they want to have restrictive policies that alienate users, they can do that."

Recent news stories have fueled the fire. When a 15-year-old boy was caught with a 9mm handgun at school in Kentucky, he told investigators he had arranged the purchase through the "Portsmouth Pickers" Facebook group.